DESCRIPTION: (Verbatim) The long-term goals of this project are to better understand epithelial stem cell biology. Epithelial stem cells are responsible for the continual regeneration and homeostasis of all self-renewing tissues such as the epidermis, hair follicle, and corneal epithelium. We originally identified epithelial stem cells in the limbal epithelium of the cornea, and in the bulge region of the outer root sheath of the hair follicle. Recently, we demonstrated that cytokeratin 15 (K15) is selectively expressed by bulge cells, and our preliminary results show that K15 is also expressed in the limbal epithelium of the cornea. Now, we have isolated the K15 promoter, and we plan to use this as a tool to study the hypothesis that bulge cells play a major role in hair follicle cycling, alopecia, wound healing, and carcinogenesis. Specifically, we plan to: 1. characterize K15 promoter activity during development, throughout the hair follicle cycle and in response to hyperproliferative stimuli. We will test the hypothesis that K15 is preferentially expressed in other sites enriched in epithelial stem cells by examining its expression in corneal epithelium as well. Our primary goal is to develop a transgenic system that can be modulated by exogenous agents (e.g., retinoids, phorbol esters, corticosteroids) so that we can study tissue compartments rich in epithelial stem cells. 2. determine whether sonic hedgehog (shh) and activated beta-catenin, known to cause basal cell carcinomas and hair follicle tumors, respectively, when expressed throughout the epidermal basal layer, cause similar or distinct tumors when targeted to the bulge cells by the K15 promoter in a transgenic system. 3. assess the role of the bulge cells in hair follicle cycling by analyzing the hair cycle in transgenic mice that over-express shh and activated beta-catenin. 4. ablate hair follicle bulge cells in adult transgenic mice carrying a K15 promoter/thymidine kinase suicide gene. This addresses the hypothesis that the bulge contains stem cells responsible for hair follicle cycling, epidermal renewal and sebaceous gland regeneration. We also plan to use this system as a model for studying scarring alopecias. Patients with disorders such as alopecia, basal cell carcinoma, hair follicle tumors, or chronic wounds may ultimately benefit from this research.